Hot gas refrigeration defrosting system

ABSTRACT

An improved dual refrigeration and defrost system having cycles of refrigeration and defrost so integrated that the heat collected from one bank of refrigerating evaporators is used for defrosting another evaporator unit with the refrigerant lines into the refrigeration chamber being reduced to a two pipe refrigerant supply line and a suction return line that permits almost all critical control components to be located outside of the refrigeration chamber to facilitate safe and convenient maintenance and repair of said control components.

United States Patent Patterson 1451 '1 23, 1972 54] HOT GAS REFRIGERATION 2,693,678 11/1954 Toothman ..62/234 DEFROSTING SYSTEM 3,184,926 5/1965 Blake ..62/278 3,316,731 5/1967 Quick ..62/278 1 InventorI Paflemn, 5511 Basswood Lane, 3,531,945 10/1970 Brennan ..62/234 Austin, Tex. 78723 [22] Filed: Dec. 30, 1970 [21] Appl. No.: 102,669

[56] References Cited UNITED STATES PATENTS Patterson ..62/278 Primary Examiner-William J. Wye Att0rneyMarion E. Shafer [57] ABSTRACT An improved dual refrigeration and defrost system having cycles of refrigeration and defrost so integrated that the heat collected from one bank of refrigerating evaporators is used for defrosting another evaporator unit with the refrigerant lines into the refrigeration chamber being reduced to a two pipe refrigerant supply line and a suction return line that permits almost all critical control components to be located outside of the refrigeration chamber to facilitate safe and convenient maintenance and repair of said control components.

1 1 Claims, 2 Drawing figures PATENTEUMAY 2 3 m2 SHLU 1 0F 2 VELT C. PATTERSON INVENTOR. BY f 1 ATTORNEY PATENTED MAY 2 31972 SHEET 2 UP 2 wwt m HQ. U

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ATTORNEY HOT GAS REFRIGERATION DEFROSTING SYSTEM BACKGROUND OF THE INVENTION Deepfreeze refrigeration compartments for long term storage of foods have been commercially available for several decades with the result that the technology involving systems for operating and defrosting refrigeration apparatus in such low temperature refrigeration chambers has become a highly elaborate and abundantly varied art. Almost from the beginning of the refrigeration art it has been conventional to locate the evaporator or equivalent cooling apparatus on the interior of the refrigeration chamber, while locating the compressor and as much of the control equipment as practical at points outside of the refrigeration chamber where they could dissipate heat without compromising the temperature within the refrigeration chamber proper. Since it has always been apparent that difficulty would be encountered in getting valves and control apparatus involving moving parts to operate reliably and smoothly within the refrigeration chamber where temperatures were low, it has always been an expressed but seldom accomplished object of the art to locate as many of said valves and control devices outside the refrigeration compartment as possible. Nevertheless, practically all combination refrigeration and defrost systems have so far employed a three pipe transmission system between the exterior refrigeration chamber. One of the input pipe lines provided for the flow of liquid refrigerant to the evaporator unit, a second input line of piping provided for the transmission of hot gas into the evaporator and associated apparatus during the defrost process and a third line or system of piping provided for a common suction return path by which spent refrigeration liquid or spent defrost gas was routed back to the external refrigeration apparatus for recycling. From the experience of the past few decades it has seemed practically inevitable that such three pipe transmission systems would almost necessarily involve a plurality of operatable control valves and control mechanisms located adjacent to the evaporator within the refrigeration chamber in order to reroute the refrigerant flow when shifting from refrigeration to defrost operations. In any event, practically all commercial systems have been marked by the presence of a plurality of actuatable valves and control mechanisms within the refrigeration chamber where they were subjected to extremes of temperature variation during the refrigeration process and the alternate defrost periods in which high temperature hot gas was routed through the evaporator system and associated apparatus to defrost the apparatus by heat from the inside without lowering the external environmental temperature of the refrigeration chamber.

The rapid alternation of temperatures involved in this shift of the refrigeration cycle to the defrost cycle and back to the refrigeration cycle again precipitated repeated contractions and expansions of all of the critical parts, valves and control mechanisms with the result that intermittent maintenance and eventual replacement of practically all control mechanisms involving parts was virtually inevitable. Since the repair of replacement of moving part control mechanisms was inevitable said parts were designed and installed by means of threaded couplings which provided for reasonable means of removal and replacement. Joints and threaded couplings, however, are in themselves a source of breakdown and disorder in refrigeration equipment where the apparatus must be subjected to alternating extremes of temperature and contraction and expansion. Working or maintenance conditions within a low temperature refrigeration chamber where the hands are quickly numbed and delicate parts are difi'rcult to handle are far from idealistic and most instances it has been impractical to remove the large quantities of frozen food stuffs from the refrigeration compartment to permit warming the refrigeration compartment to more reasonable working temperatures. If the equipment breakdown involved a leak in one of the valves or control mechanisms or in one of the threaded joints in the refrigeration chamber with the result that ammonia or other poisonous refrigerant gas escaped into the refrigeration compartment there was resultant danger of contaminating food stored in said refrigeration compartment at the same time that maintenance or repair working conditions within the refrigeration compartment were seriously aggravated. A worker attempting to wear a gas mask with goggles to protect his eyes and breathing processes against refrigerant gas within the refrigeration chamber quickly found that the combination of numbing cold and difficulty with impaired vision from the fogging of inconvenient goggles drastically limited the effective working time available to a maintenance man within the refrigeration compartment. Even a cursory examination of the prior art will quickly disclose that something more needs to be done toward simplification of that part of the refrigeration apparatus that must be installed within the refrigeration chamber and that something more must be done toward removing all valves and moving part mechanisms that require intermittent maintenance or replacement out of the refrigeration compartment to an exterior location where they may be operated, maintained and repaired under more favorable and more comfortable working conditions.

OBJECTS OF THE INVENTION A primary object of this invention is to provide an improved and reduced arrangement of component parts in order to minimize the possibility of breakdown by moving temperature sensitive control elements and parts to locations outside of the refrigeration compartment where they will not be exposed to extremes of temperature.

Another object of this invention is to move all of the actuatable hot gas control valves involving moving parts to locations outside of the refrigeration chamber where they can operate more reliably and more efficiently under normal temperature conditions.

A further objective of this Invention is to minimize the danger of spoilage or contamination of foodstuffs or other refrigerated items during maintenance or breakdown by moving control equipment and parts that may leak refrigerant gas or that may require servicing to locations outside of the refrigeration chamber.

Another object of the Invention is to maximize the availability and access of the component parts in the possible case of a breakdown.

Another object is to minimize the danger to and to improve the working conditions of maintenance personnel required to service or repair damages or worn parts of said refrigeration system by removing parts susceptible to breakdown to a more favorable environmental location where they can be repaired under more comfortable and more efficient working conditions.

A further object is to provide a combination refrigerationdefrost defrost system that accelerates the rate at which defrosting occurs.

. Another object of this Invention is to provide a more effcient, simple, and automatic piping and control arrangement by which both the liquid refrigerant and the hot defrost gas are piped into and out of the refrigeration chamber by means of a simple two pipe transmission system.

Still another object is to provide for selective defrosting of a particular evaporator while the remainder of the evaporator units in a given refrigeration chamber continue with their normal refrigeration processes.

A still further object of the Invention is to devise a refrigeration-defrost system in which the used or heated refrigerant from the cooling evaporator units is separated out and processed into hot gas for use in the evaporators being defrosted.

Still a further object of this Invention is to provide for efficient, proportionate and simultaneous distribution of hot gas to both the evaporator unit and the associated drain pan coil by metering and controlling the division of hot gas between said drain pan coil and the evaporator unit being defrosted.

A still further objective of the Invention is to provide an absolutely positive means of preventing any liquid refrigerant from reaching or entering the suction input to the hot gas compressor by means of a preliminary separation of hot gas from the liquid refrigerant in a combination surge drum separater and pump receiver.

These and other objects and advantages of this Invention will become apparent through the consideration of the following description and appended Claims in conjunction with the attached Drawings in which:

DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS FIG. 1 is a diagrammatic illustration of an overall preferred embodiment of my Invention.

FIG. 2 is an enlarged diagrammatic illustration of that portion of one system of said refrigeration and defrost apparatus that is situated inside of the refrigeration chamber showing a system of two ganged evaporators connected in parallel for simultaneous refrigeration or defrosting of both of said evaporator units.

In describing one selected form of preferred embodiment of this Invention as shown in the Drawings and this Specification, specific terms and components are used for clarity. However, it is not intended to limit the claimed Invention to the specific form, components, or construction shown and it is to be understood that the specific terms in this illustration of the invention are intended to include all technical equivalents which operate in a similar manner to accomplish a similar purpose.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT OF INVENTION The dual combination refrigeration and hot gas defrosting system contemplated by this Invention and as described herein contemplates a large refrigeration storage chamber 11 surrounded by appropriate insulated walls 12 in which the designer will of course provide appropriate doors and customary lighting and drainage facilities with said refrigeration chamber 11 being provided with a plurality of evaporator units 13-13 installed at convenient locations within said refrigeration chamber 11 together with an associated refrigeration support system including refrigerant recirculation apparatus and a hot gas compressor system located in an equipment room or other appropriate location convenient to but otherwise outside of said refrigeration chamber 11 as suggested and illustrated in FIG. 1 of the Drawings herein. Although the Invention contemplates but is not necessarily restricted to a single external refrigeration support system including appropriate control apparatus and transmission pipe lines into the refrigeration chamber it is contemplated that the plurality of refrigeration evaporator units 13-13 within refrigeration chamber 11 will be organized into a plurality of refrigeration evaporator systems such as that designated as evaporator system A and that designated as evaporator system B in FIG. 1 of the Drawings with each of said systems of evaporator units having at least one evaporator unit within the system although it is contemplated that in large food locker or deepfreeze storage facility plants that each of said systems of evaporators will be composed of a plurality of such evaporator units connected in parallel as illustrated in FIG. 2 of the Drawings so that all of the evaporator units within a single system of evaporators will be programmed for simultaneous refrigeration cycles of operation and will be simultaneously defrosted although other evaporators in the same refrigeration chamber that are part of other evaporation systems,may continue to function without interruption of their refrigeration operation.

Each of said evaporator units 13-13 is provided with an appropriate distribution manifold 14, a suction-collection manifold 15 with a plurality of evaporation coils 16-16 connected between distribution manifold 14 and said collection manifold 15 with sized flow control orifices 17-17 being interposed between the end of each evaporation coil 16 and distribution manifold 14 in such manner that refrigerant or gas flow from distribution manifold 14 into each of said evaporation coils 16-16 or that flow from each of the evaporation coils into said distribution manifold 14 has to be channeled through and the volume of such flow controlled or regulated by the size of said control orifices 17-17. It will be readily appreciated that the sizing of said flow control orifices 17-17 will regulate the division or distribution of refrigerant or defrost gas in equal quantities into each of said evaporation coils 16-16 while slightly pressurized liquid refrigerant being throttled or squirted through each of said sized flow control orifices 17-17 into the low pressure space inside of each of the evaporator coils 16-16 will be largely precipitated into boiling vapor as it expands and spreads through said orifices 17-17 and then flows through said evaporation coils 16-16 absorbing heat from the surrounding refrigeration chamber as said refrigerant travels through said evaporation coils. The effectiveness of such refrigeration process will obviously be enhanced by the application of increased suction or a vacuum through suction-collection manifold 15 and parallel coils 16- 16 so that there is a rapid drop in pressure as the refrigerant travels from distribution manifold 14 through orifices 17- 17 and it is a part of the scheme of this Invention to provide for an effectively large pressure drop through control orifices 17- 17 by enhancing the suction pull on the low end of each evaporator by providing a low resistance path back to the external refrigeration apparatus and by combining the simultaneous and cumulative pull of two pumps applying suction to the low end of said refrigeration system.

When evaporator units 13-13 are defrosting, the melting ice will convert into water and drip into drain pan 18 and from drain pan 18 to disposition points outside of said refrigeration chamber 11 by means of heated drain pan outlet pipe 19 which is a convenient and customary manner of handling the disposition of moisture and ice collected upon the exterior surfaces of said refrigeration apparatus. Since it is common for said drain pan and for associated outlet plumbing to freeze during the refrigeration cycle in low temperature or deepfreeze equipment it is customary to provide said drip-drain pan and associated outlet plumbing with an appropriate defrost drain pan heating coil 20 which is often connected in series with the distribution routing for evaporator unit 13 so that the hot gas employed for defrosting evaporator 13 also flows through and defrosts drain pan 18 and associated drain equipment. Since drain pan 18 needs to be unfrozen before it can effectively receive and convey away melted ice drained off of evaporator unit 13 it is customary to direct the hot defrost gas into the refrigeration chamber 11 through a separate hot gas pipe system which feeds said hot defrost gas into the drain pan heating coil 20 first and from there into evaporator unit 13 so that said drain pan 18 is thawed out at the very beginning of the defrost cycle. The result of such a series feed arrangement during the defrost cycle results in all of the defrost hot gas being throttled through drain pan heating coil 20 before it goes to evaporator unit 13 and all of said hot defrost gas continues to be uselessly channeled through drain pan heating coil 20 all through the defrost cycle even after said drip-drain pan 18 and associated plumbing have been thawed out and made serviceable. Such systems in the past have practically always involved the use of a three pipe transmission system into the refrigeration chamber in which one pipe was employed to direct liquid refrigerant into each of the evaporator unit 13-13, a second pipe line was employed to convey hot defrost gas into said refrigeration chamber and thence to drain pan heating coil 20 from which said hot gas was further channeled into the coils of evaporator unit 13 for defrosting and thence back to the external support and recirculation equipment by means of a common suction-retum pipe line which involved three pipes into the refrigeration chamber together with elaborate control apparatus for rerouting or shutting off the supply of liquid refrigerant during defrosting and opening up routing paths for said hot gas during the defrost cycle. Each of these pipes with numerous joints and connection and a considerable plurality of moving part control valves were operated in the refrigeration chambers hostile low temperature environment with rapid alternations of high and low temperature in converting from the refrigeration cycle to the alternate defrost cycle and back with consequent dangers of malfunction of many of said parts and valves together with even more serious risk of breaks or leaks in said piping control valves which often permitted toxic refrigerant vapors to escape into the refrigeration chamber where said toxic refrigerant vapors could contaminate food products stored in said refrigeration chamber and added a further danger to the frigid hostile environment of said refrigeration chamber for servicemen who might be sent into the refrigeration chamber to repair such leaks or malfunctioning refrigeration equipment.

In order to eliminate or minimize many of these risks the lnventor of the apparatus described herein calls for connecting drain pan heating coil in parallel with the customary refrigerant leads to and from evaporator unit 13 by means of drain pan heating coil supply lines 21-22 and by providing a drain pan heating throttle control orifice 23 connected in series with said drain pan heating coil supply lines 21-22 to control and limit the flow of hot defrost gas through said drain pan heating coil 20. Said sized drain pan heating coil throttle control orifice 23 is of such a selected size or volume with respect to the size of paralleled flow control orifices 17 in evaporator unit 13 as to permit only that amount of hot defrost gas to be channeled through drain pan heating coil 20 as is absolutely necessary to melt the ice on and in defrost drip-drain pan l3 and its associated outlet plumbing and to keep said drip-drain pan operative throughout the defrost cycle with resultant minimization of wasted defrost gas to said drain pan heating coil 20. In effect the comparative sizing of flow control orifices l7-l7 in evaporator versus the size of throttle control orifice 23 in the parallel feed line to drain pan heating coil 20 results in a controlled division of the supply of hot defrost gas between the evaporator 13 and drain pan heating coil 20 providing for a more efficient and economical application of the available supply of hot defrost gas.

If drip drain pan 18 is to be connected in parallel with the input and output leads to evaporator 13 then some means must be provided for, preventing the useless channelling of liquid refrigerant to drip-drain pan 18 during the refrigeration cycle. in the arrangement of apparatus proposed by the Inventor herein this have been accomplished by connecting in series with one of the drain pan heating coil supply lines 21-22, a one way check valve 24 which has a minimum of moving parts and requires no external controls or actuation other than response to internal fluid pressure in the line which automatically blocks the refrigerant attempting to flow in one direction but permits the flow of hot gas in the reverse direction during the defrost cycle. Thus by connection evaporating unit 13 and drain pan heating coil 20 in parallel with a one way check valve 24 in series with one of the leads to the drain pan heating coil and by providing for the reversal of the direction of flow when hot gas is pumped through the refrigeration apparatus during the defrost cycle it has been made possible to route hot gas through both evaporator unit 13 and drain pan heating coil 20 during the defrost cycle while permitting liquid refrigerant to flow in the reverse direction through evaporator unit 13 only during the refrigeration cycle by means of a single pressure operated one way check valve involving a minimum of parts so that the possibility of danger of breakdown of component parts and control valves within the refrigeration chamber has been reduced to an absolute minimum by this arrangement which has removed all but one reasonably fool proof check valve out of the refrigeration chamber.

One of the features of the refrigeration-defrost apparatus recommended by the Inventor herein is that'each system of evaporators is served by a two pipe system of refrigerant supply lines into the refrigeration chamber by means of which liquid refrigerant is channeled into said refrigeration chamber and to evaporator units 13-13 of one system of evaporators by means of refrigerant supply transmission line 25 while the spent or used refrigerant droplets and vapor are routed back to the external refrigerant recirculation apparatus by means of a large diameter insulated low pressure refrigerant return-suction line 26. Since the difference in temperature between the liquid refrigerant flowing inside refrigerant supply transmission line 25 and the environmental temperature within refrigeration chamber 11 is relatively small conventional refrigerant piping may be employed for said refrigerant supply transmission line 25, and that portion of said transmission line 25 within the interior of refrigeration chamber 11 should be provided with exterior covering of insulation material and it would be advisable even to provide an insulated jacket or covering to that part of the transmission line outside of the refrigeration chamber. However, the Inventor prefers and recommends that retum-suction line 26 be fabricated from a pipe of considerably larger diameter than that employed for refrigerant transmission line 25 so that the suction pull from the refrigerant pump and the compressor in the refrigerant recirculation system will be able to move the returning refrigerant vapor with minimum pressure drop and minimum friction, if any, with the interior walls of return line 26. It is also recommended that all of that part of return line 26 that is situated within refrigeration chamber 11 be provided with an exterior insulated covering 27 or insulated jacket so that heat collected from refrigeration chamber 11 by the refrigerant vapor as it travels through evaporator units 13-13 will not be retransferred into said refrigeration chamber 11 through the walls of suction-return pipe line 26.

During the defrost cycle, the direction of flow will be reversed and hot defrost gas will be directed into refrigeration chamber 11 and evaporator unit 13 via means of pipe line 26. Again, high pressure hot gas can be moved into and through refrigeration chamber 11 more effectively and will less pressure loss it it is moved through large diameter pipe line 26. This of course requires that the direction of flow through the two transmission pipe lines 25 and 26 be reversed during the defrost cycle and, as will be explained later, control valves have been provided by which this reversal of the direction of flow can be accomplished. It should also be pointed out that it is transmission line 25 and 26 carrying hot gas or refrigerant into low temperature refrigeration chamber 11 are susceptible to leaks by way of cracks or rupture as a result of shock and expansion and extreme differential temperature between the defrost gas inside the pipe and the very cold air in the refrigeration chamber and that said transmission pipe lines are susceptible to damage by shock when the line is accidentally bumped by freight loaded dollies or lift trucks transporting products in or out of the refrigerated storage room. By fabricating said suction-return transmission line 26 out of larger diameter pipe with all welded connections and providing at least said large diameter pipe line 26 with an appropriate insulation jacket 27 said pipe line is better protected against heat loss and contraction-expansion problems and against the hazard of shock when accidentally contacted or struck by moving loading equipment.

Leaving aside the control equipment and valves and rerouting mechanism for the present, suction-return transmission line 26 continues through suction solenoid valve 43, thence through suction-return line 28 by which it returns through its own input into the surge drum and pump receiver 29 portions of said refrigerant circulation recirculation apparatus include a liquid refrigerant pump 30, surge drum and pump receiver 29 and associated hardware and connecting lines. Surge drum and pump receiver 29 is a reservoir adapted to receive and separate the liquid refrigerant and gas from each other, said surge drum 29 being provided with a depending gravity fed liquid collecting sub-reservoir 31 designed to maintain an uninterrupted constant level head of liquid refrigerant 32 into liquid refrigerant pump 30. The input from suction-return line 28 into said surge drum and pump receiver 29 delivers said returning refrigerant vapor into an upper portion of surge drum 29 at a point above the contemplated liquid level. The liquid portion of said refrigerant 32 settles to the bottom of surge drum 29 from whence it flows by gravity into a stand pipe sub-reservoir 31 which depends from the bottom of surge drum 29 to maintain a supply head of liquid refrigerant 32 for delivery to liquid refrigerant pump 30 as previously mentioned. As stated, gravity pulls the liquid refrigerant to the bottom of surge drum 29 whereas the gaseous portion of said returning refrigerant vapor rises to the top of surge drum 29 where it may be removed by means of gas output suction supply line 33 for transmission to a hot gas compressor thus completely separating the gas and liquid refrigerant. This output vent or exit to said suction supply line 33 is located at the very top of surge drum 29 so that absolutely no liquid can reach said output vent for transmission to the hot gas compressor. The output from dry hot gas compressor 34 is delivered to compressor discharge line 35 which in turn connects to defrost line 36 which may or may not be delivering hot defrost gas at any particular moment to one or more of the evaporator units in the system that may need defrosting. If all the hot gas output from compressor 34 is not used for defrosting purposes, then the surplus is diverted through a parallel takeoff from compressor discharge line 35 into a condenser 37 line where much of it converts back into a liquid refrigerant. Said condenser 37 in turn empties into high pressure receiver 38 where the portion of said refrigerant being condensed back into liquid can collect. The output from high pressure receiver 38 in turn connects through refrigerant supply line 39 to provide a return path for condensed liquid refrigerant back into surge drum and pump receiver reservoir 29. The input from refrigerant supply line 39 into said surge reservoir 29 is controlled or metered by a float actuated supply valve 40 which operates in a conventional manner to meter and maintain a constant level of liquid refrigerant in surge drum 29 by opening float actuated supply valve 40 when the supply of liquid refrigerant falls below a predetermined level and alternately closing said float actuated supply valve 40 thereby shutting off the flow of liquid refrigerant from high pressure receiver 38 when the supply of liquid refrigerant in surge drum 29 has been restored to its proper predetermined level.

Returning to the liquid refrigerant pump 30 portion of said refrigerant recirculation apparatus said liquid refrigerant pump 30 may be selected solely on the basis of its liquid pumping qualities and greater efficiency thereby achieved in as much as the system described eliminates the possibility of refrigerant vapor of gas bubbles reaching said refrigerant pump since the very efficient system of gas-liquid separation in pump receiver and surge drum 29 previously described assures that only condensed liquid refrigerant will be channelled into liquid collecting sub-reservoir 31 for input into said liquid refrigerant pump 30. The output from liquid refrigerant pump 30 is delivered to liquid refrigerant supply distribution line 41 which in turn connects through appropriate solonoid control valves to feed said supply of liquid refrigerant into the through parallel evaporator supply lines 25-25 to each of the operating systems of evaporator units 13-13 as previously described.

We will start our examination and description of the control system by defining the normal or refrigeration-operation position of each of the major control valves. As previously explained, liquid refrigerant is delivered by refrigerant pump 30 through liquid refrigerant supply distribution line 41 through normally open liquid refrigerant solonoid valves 42-42 into evaporator supply lines 25-25 for distribution to each of the refrigerating evaporators 13-13. Said liquid refrigerant flows via means previously described through evaporators 13-13 and thence via suction-return line 26 through normally open suction solonoid valve 43 and back to the refrigerant recirculation system via means of suction-return line 28 as previously explained. During the refrigeration cycle hot vapor solonoid valves 44-44 is normally closed to prevent hot defrost gas from getting into a suction return line from one of the evaporator systems still engaged in the refrigeration process.

The remaining significant control valve is a normally closed pressure relief valve 45 in defrost cross line 46-46 which provides a means of rerouting used defrost gas back to surge drum 29 after the direction of flow through transmission pipe lines 25 and 26 have been reversed.

Although surge drum and pump receiver 29 with liquid refrigerant pump 30 and compressor 34 together with condenser 37 and high pressure receiver 38 provide a common refrigeration support system supplying liquid refrigerant and hot gas for all of the several systems of evaporators that may be operated in the installation it should be noted that each system of evaporators 13-13 is provided with its own two pipe pair of refrigerant transmission lines 25 and 26 and that each of said evaporator systems and associated pair of trans mission lines 25-26 is provided with a separate control system to control, space and stagger the several defrost cycles so that only one system of evaporators is being defrosted at a time. In the lnventors first experimental prototype of this refrigeration system, said staggered programming of the several defrost cycles was accomplished by providing each evaporator control system with a clock 48 controlled master timer unit 47 which is response to electrical signals from said master timer control unit 47 during the defrost cycle reversed the normal operating conditions for solonoid conditions for solonoid controlled valves 42, 43, and 44. Normally closed hot vapor solonoid valve 44 for one of the systems of evaporators is opened dur ing the defrost cycle by electric control signals from master timer unit 47 which permits hot defrost gas to flow from compressor 34 through hot gas lines 35, 36 and into transmission line 26 for distribution to evaporators in that system or bank of paralleled evaporators l3-13 that are to be defrosted. At the same time, normally open suction solonoid valve 43 is closed in response to electrical control signals from the master timer unit 47 for the system being defrosted to block and prevent the incoming supply of hot defrost gas into transmission line 26 from being sucked back through suction return line 28 to surge drum and pump receiver 29. Also at the same time, defrost signals from master timer control unit 47 for the system being defrosted closed normally open liquid refrigerant solonoid valve 42 to prevent further cold liquid refrigerant from being pumped into transmission line 25 or those evaporators 13-13 that are are engaged in the defrost process. Since the direction of flow has been reversed during the defrost cycle and compressed hot gas is now flowing through large diameter transmission line 26 into evaporators 13-13 and returning through transmission pipe line 25 to now closed liquid refrigerant solonoid valve 42 an alternate return path for said used defrost gas must be provided and this is accomplished by providing a defrost cross line 46-46 between transmission line 25 and suction-return line 28. Said defrost cross line 46-46 flows through a normally closed pressure operated pressure relief valve 45 which keeps said cross line blocked off and inoperative at the low pressures involved during the normal refrigeration cycle. However, during the defrost cycle with solonoid valves 42 and 43 closed pressure relief valve 45 is subjected to a low pressure pull on its low end side from suction-return line 28 to refrigerant pump 30 while an increased pressure from returning defrost gas through transmission line 25 is applied to the upper side of said pressure relief valve 45. When the increase in differential pressure across relief valve 45 rises above a preset actuation point said pressure relief valve 45 pops open and condensed defrost gas is allowed to flow through the alternate return route from transmission line 25, through defrost cross line 46-46 through now open pressure relief valve 45 and thence via suction-retum line 28 to surge drum and pump receiver 29. During the refrigeration cycle, normally closed one way check valve 24 blocks the flow of any liquid refrigerant through drain pan heating coil 20 as previously explained but during the alternate defrost cycle when the defrost hot gas flows in the reverse direction, part of said defrost gas can flow through drain pan heating coil 20, through one way check valve 24 which is open to flow in this reverse direction and via supply line 22 back to transmission line 25 with the metered division of hot gas between evaporator 13-13 and drain pan heating coil being controlled by comparative size of flow control orifice 23 in series with the supply lines to said drain pan heating coil 20 and the comparative size of the several flow control orifices 17-17 that meter and control the flow of condensed defrost gas through the several parallel paths through evaporator 13 as previously explained.

Note that the described system of two pipe transmission lines to each system or gang of parallel evaporator units 13- 13 permits the programmed master control units 47 and associated control valves 42, 43, 44 and 45 for each system of evaporators to be grouped and installed at a location remote from and outside of refrigeration chamber 11 .so that they are readily accessible for maintenance and repair service under more favorable operating and working conditions.

OPERATION All of the sub systems within this refrigeration system start and return to surge drum and pump receiver 29 in the common refrigeration support system which receives returning gas and refrigerant liquid and vapor from the several evaporators 13-13 and divides the returning fluid into gas and liquid routing the liquid refrigerant to a pump for recirculation and routing the gas to a compressor 34 to provide hot gas for defrostjng. No effort has been made to illustrate or describe sources of electric or motive power for pump 30 or compressor 34 nor control mechanisms for turning said pump and compressor off and on as needed since there is an abundance of commercially available devices and hardware for such purposes and such master control starting off-on programming equipment for said pump and compressor are an assumed part of the equipment-and it is assumed that the system is turned on and in operation.

At a given time liquid refrigerant from surge drum and pump receiver 29 will be pumped by pump 30 through liquid refrigerant distribution supply line 41 through open control valves 42-42 and via transmission lines -25 to such evaporator systems as are refrigerating at that time with liquid refrigerant also being channeled to such additional evaporator units 13-13 as may be banked or ganged or connected in a parallel system A or into a parallel system B, etc., as partially illustrated in FIG. 2 of the Drawings herein, and thence back through return transmission line 26 and suction-retum line 28 to common surge drum and pump receiver 29.

Part of such returning refrigerant vapor will have absorbed sufficient heat in travelling through refrigerating evaporators 13-13 to have been converted into a gaseous state. The warmed gaseous part of said returning refrigerant fluid will be separated from the liquid refrigerant in surge drum 29 with said warm gas being pulled out of the upper part of surge drum 29 by suction from compressor 34 to provide compressed hot gas for defrosting purposes. The detailed routes of flow and operation of the several sub systems employed in refrigeration and defrosting have been covered in connection with the detailed description of the preferred embodiment of the Invention described above and need not be repeated in detail at this point beyond recapitulating over all generalizations. Note that if evaporator system A is being defrosted at a given time in response to control signals from master control unit 47 and evaporator system B, which may be a ganged system of a plurality of parallel connected evaporator units 13-13 as illustrated in FIG. 2 of the Drawings, is in normal refrigerating operation that heat absorbed into the refrigerant fluid while passing through refrigerating evaporators 13-13 in system B will be separated out with the gas in surge drum 29 and compressed by compressor 34 to provide hot gas for defrosting the plurality of evaporators 13-13 that may be ganged into parallel connected evaporators in evaporator system A. Thus in a large system heat absorbed by the cooling evaporators in one system of evaporators may be collected and employed to assist in providing hot defrost gas for those evaporators being defrosted in another system of evaporators. By programming the several master timer units 47 to provide staggered or successive defrost cycles so that only one system of evaporators 13-13 is defrosted at a time and all of the remaining refrigerating systems of evaporators provide collectively pooled gas and heat for the single system being defrosted a considerable improvement in overall efficiency can be achieved.

ADVANTAGES OF THE INVENTION A significant advantage of the Invention described herein is that it provides a means by which a plurality of systems of evaporators can be defrosted in staggered relays permitting a larger number of evaporator units to be more efficiently operated from a single system of support equipment without interrupting the overall refrigeration process in the refrigeration chamber.

Another advantage of the refrigeration system contemplated by this Invention is that in a large system the heat collected by passage of the refrigeration fluid through the refrigerating evaporator units can be collected and pooled to help provide hot defrost gas for the evaporators being defrosted.

A primary advantage of this Invention is that it provides an improved and reduced arrangement of component parts and in order to minimize the possibility of breakdown it moves temperature sensitive control elements and parts to locations outside of the refrigeration compartment where they will not be exposed to extremes of temperature.

Another object of this Invention is to move all of the actuatable hot gas control valves involving moving parts to loca tions outside of the refrigeration chamber where they can operate more reliably and more efficiently under normal temperature conditions.

By routing the supply of liquid refrigerant through a simplified pair of supply pipe lines and through the refrigerating evaporators in one direction and then reversing the direction of flow when hot gas is pumped through the evaporators and associated equipment during the defrost cycle it is possible to block the flow of liquid refrigerant through the drain pan heating coil during the refrigeration cycle by means of a single simple one way check valve in the refrigeration chamber while permitting hot defrost gas to freely pass through said check valve in the reverse direction during the defrost cycle.

A further advantage of this Invention is that it minimizes the danger of spoilage or contamination of foodstuffs or other refrigerated items during maintenance or breakdown by moving control equipment and parts that may leak refrigerant gas or that may require servicing to locations outside of the refrigeration chamber.

Another advantage of the Invention is that it maximized the availability and accessability of the critical component parts and controls that may require servicing in possible cases of a breakdown.

Another advantage is that the Invention minimizes dangers to and improves working conditions of maintenance personnel required to service or repair damages or worn parts of said refrigeration system by removing parts susceptible to breakdown to a more favorable environmental location where thy can be repaired under more comfortable and more efficient working conditions.

A further advantage of the Invention is that it provides a combination refrigeration-defrost system that accelerates the rate at which defrosting can be achieved.

Another advantage of this Invention is to provide a more efficient, simple, and automatic piping and control arrangement by which both the liquid refrigerant and the hot defrost gas are piped into and out of the refrigeration chamber by means of a simple two pipe transmission system.

Still another advantage of the Invention is that it provides for selective defrosting of a particular evaporator while the remainder of the evaporator units in a given refrigeration chamber continue with their normal refrigeration processes.

Still a further advantage of this Invention is that it provides for efficient, proportionate and simultaneous distribution of hot gas to both the evaporator unit and the associated drain pan coil being defrosted by metering and controlling the division of hot gas between said drain pan coil and the evaporator unit.

A still further advantage of the Invention is to provide an absolutely positive means of preventing any liquid refrigerant from reaching or entering the suction input to the hot gas compressor by means of a preliminary separation of hot gas from the liquid refrigerant by means of an improved combination surge drum separator and pump receiver.

By a preliminary separation of gaseous refrigerant only from the liquid refrigerant in the surge drum and pump receiver part of the refrigerant recirculation apparatus this Inventor has provided a highly reliable system of separating out and routing dry gas only to the hot gas compressor which permits the use of a smaller and and much more efficient hot gas compressor since the operation of the compressor is not compromised by the presence of liquid or wetted surfaces.

Although this specification describes but a single embodiment of the Invention with certain applications thereof, it should be understood that structural or material rearrangements of adequate or equivalent parts, substitutions of equivalent functional elements and other modifications in structure can be made and other applications devised without departing from the spirit and scope of my Invention. I therefore desire that the description and drawings herein be regarded as only an illustration of my Invention and that the Invention be regarded as limited only as set forth in the following claims, or as required by the prior art. Having thus described my Invention,

I claim:

1. In a deep freeze refrigeration facility having an insulated refrigeration chamber for storing materials at very low temperatures, with the heat absorbing apparatus located inside of the refrigeration chamber and associated support apparatus situated at convenient locations outside of the refrigeration chamber, an improved system of combination refrigeration and hot gas defrosting apparatus, said improved system comprising:

A. a plurality of refrigeration evaporator units situated in said refrigeration chamber with each of said evaporators being provided with l. a distribution manifold,

2. a suction-collection manifold,

3. a plurality of evaporation coils connected between the distribution manifold and the collection manifold and 4. flow control orifices between each of the evaporation coils and one of the manifolds; B. a defrost drip-drain pan situated below the evaporator; C. a drain pan heating coil connected in parallel with the refrigerant leads to and from said evaporator unit; D. check valve means in the connecting lines to the drain pan heating coil for automatically preventing flow of refrigerant through the drain pan heating coil during refrigeration cycle while permitting the flow of hot gas in the reverse direction during defrost cycle; E. control means of apportioning the division of hot gas supply between the evaporator and the drain pan heating coil during the defrost cycle; F. a two pipe system of refrigerant supply lines into the refrigeration chamber comprising 1. a refrigerant supply transmission line to at least two evaporator units and 2. a low pressure return-suction line from the evaporator units to appropriate refrigerant recirculation apparatus;

G. means for receiving the recirculating the liquid refrigerant received from the evaporators;

H. means for separating out the gaseous portion of the returning refrigerant and compressing it into a hot gas for hot gas defrosting of the several evaporator units;

I. timer controlled means for selectively shutting off the refrigerant supply to that part of the evaporator units selected for defrosting;

J. timer controlled means for closing off the usual evaporator return line from the evaporators being defrosted to the refrigerant recirculation apparatus;

K. control means for routing compressed hot gas into the large diameter refrigerant transmission line to the evaporator units selected for defrosting during the defrost cycle; and

L. control means for rerouting the used defrost gas back to the refrigerant recirculation apparatus.

2. The improved system of combination refrigeration and hot gas defrosting apparatus described in claim 1 in which the controlled and apportioning and division of hot gas between the evaporator and the drain pan heating coil during the defrost cycle is accomplished by means of sized control orifices in each of the parallel branch lines by which defrost gas is released into the several lines to be defrosted.

3. The improved system of combination refrigeration and hot gas defrosting apparatus described in claim 1 in which the hot gas line and low pressure return-suction line from the evaporator unit is a large diameter pipe insulated through at least that part of its length that is inside of the refrigeration chamber to better protect said line from breaks precipitated by shock and extreme differences between internal and external temperature during the defrost process.

4. The improved system of combination refrigeration and hot gas defrosting apparatus described in claim 1 in which the refrigerant recirculation apparatus includes:

A. a surge drum and pump receiver adapted to separate liquid refrigerant and gas having 1. a gravity fed liquid collecting sub-reservoir to maintain an uninterrupted head of liquid refrigerant to a liquid refrigerant pump,

2. an input into said surge drum from the refrigerant low pressure suction return lines from the evaporator units,

3. a gas only output suction supply line from the upper portion of the surge drum with said gas output supply line leading to a hot gas compressor,

4. a metered liquid input into said surge drum from liquid return supply means from a condenser and high pressure receiver off of the hot gas compressor discharge line, and

5. a float actuated supply valve to meter and maintain a constant level of liquid refrigerant in said surge drum; and

B. a liquid refrigerant pump to supply liquid refrigerant to the several evaporator units with a. input connections from said surge drum and pump receiver and b. output leads to the refrigerant transmission supply lines to each of the several evaporator units to be supplied.

5. The improved system of combination refrigeration and hot gas defrosting apparatus described in claim 1 in which the plurality of evaporator units are divided into at least two systems of evaporators with the evaporator units within each system connected in parallel.

6. The improved system of combination refrigeration and hot gas defrosting apparatus described in claim 5 with at least two sets of time clock control means and associated control valves actuating the controlling alternating cycles of refrigeration and defrosting in each system of evaporator units.

7. The improved system of combination refrigeration and hot gas defrosting apparatus described in claim 6 in which the several time clock control means for the several evaporator systems are programmed in such manner that only one system of evaporators is defrosted at a time.

8. An improved combination refrigeration and hot gas defrosting system comprising:

A. an insulated refrigeration chamber;

B. a plurality of refrigeration evaporator units situated in said refrigeration chamber with each of said evaporators being provided with l. a distribution manifold 2. a suction-collection manifold,

3. a plurality of evaporation coils connected between the distribution manifold and 4. sized flow control orifices between each of the evaporation coils and one of the manifolds;

C. a defrost drip-drain pan situated below the evaporator;

D. a drain pan heating coil connected in parallel with the refrigerant leads to and from the associated evaporator unit;

E. check valve means in the defrost gas line to the drain pan heating coil for automatically preventing flow of refrigerant through the drip pan heating coil during refrigeration cycle while permitting the flow of hot gas in the reverse direction during defrost cycle;

F. sized orifice control means of apportioning the division of hot gas supply between the evaporator and the associated drain pan heating coil during the defrost cycle;

G. a two pipe system of refrigerant supply lines into the refrigeration chamber comprising 1. a refrigerant supply transmission line to at least two evaporator units, and

2. a large diameter insulated low pressure refrigerant retum-suction line from the evaporator units to appropriate refrigerant recirculation apparatus;

l-l. refrigerant recirculation apparatus including 1. a surge drum and pump receiver adapted to separate liquid refrigerant and gas and having a. a gravity fed liquid collecting sub-reservoir to maintain an uninterrupted and constant head of liquid refrigerant to a liquid refrigerant pump,

b. an input into said surge drum from the refrigerant low pressure suction return lines from the evaporator units,

c. a gas only output suction supply line leading to a hot gas compressor,

d. a metered liquid input into said surge drum from liquid return supply means from a condenser and high pressure receiver off of the hot gas compresser discharge line, and

e. a float actuated supply valve to meter maintain a constant level of liquid refrigerant in said surge drum;

2. a liquid refrigerant pump to supply liquid refrigerant to the several evaporator units with a. input connections from said surge drum and pump receiver and b. output leads to the refrigerant transmission supply lines to each of the several evaporator units to be supplied; 1. a dry gas compressor 1. connected to the gas output supply line from the surge drum and pump receiver unit and adapted to pull a partial vacuum on the low side of the refrigeration system, 2. with compressor discharge line connections to supply pressurized hot gas to a. a condenser system and b. to the hot gas defrost leads to the evaporator units;

J. a high pressure condenser and receiver system with its input connected to the hot gas compressor discharge line and the output from said high pressure receiver reservoir connected back to the return liquid input into the surge drum and pump receiver;

K. a defrost cycle control system for each system of evaporator units with said defrost cycle control system having 1. a master clock timer unit connected to and programed to control and a. close a suction solonoid valve in the return line from the evaporators being defrosted,

b. open a hot vapor solonoid valve routing hot gas from the compressor into the suction return line from each of the evaporator units to be defrosted and c. close a liquid refrigerant solonoid valve in the liquid refrigerant supply lines to suspend the flow of liquid refrigerant to the evaporator unit being defrosted, and 2. a pressure operated relief valve in a defrost cross line between the closed off liquid refrigerant supply line and the low pressure suction return line by which the defrost gas is routed back to the surge drum and pump receiver for further recycling.

9. The improved system of combination refrigeration and hot gas defrosting apparatus described in claim 8 in which the plurality of evaporator unit are divided into at least two systems of evaporators with the evaporator units within each system connected in parallel.

10. The improved system of combination refrigeration and hot gas defrosting apparatus described in claim 9 with at least two sets of time clock control means and associated control valves separately actuating and controlling alternating cycles of refrigeration and defrosting in each system of evaporator units.

11. The improved system of combination refrigeration and hot gas defrosting apparatus described in claim 10 in which the several time clock control means for the several evaporator systems are programed in such manner that only one system of evaporators is defrosted at a time. 

1. In a deep freeze refrigeration facility having an insulated refrigeration chamber for storing materials at very low temperatures, with the heat absorbing apparatus located inside of the refrigeration chamber and associated support apparatus situated at convenient locations outside of the refrigeration chamber, an improved system of combination refrigeration and hot gas defrosting apparatus, said improved system comprising: A. a plurality of refrigeration evaporator units situated in said refrigeration chamber with each of said evaporators being provided with
 1. a distribution manifold,
 2. a suction-collection manifold,
 3. a plurality of evaporation coils connected between the distribution manifold and the collection manifold and
 4. flow control orifices between each of the evaporation coils and one of the manifolds; B. a defrost drip-drain pan situated below the evaporator; C. a drain pan heating coil connected in parallel with the refrigerant leads to and from said evaporator unit; D. check valve means in the connecting lines to the drain pan heating coil for automatically preventing flow of refrigerant through the drain pan heating coil during refrigeration cycle while permitting the flow of hot gas in the reverse direction during defrost cycle; E. control means of apportioning the division of hot gas supply between the evaporator and the drain pan heating coil during the defrost cycle; F. a two pipe system of refrigerant supply lines into the refrigeration chamber comprising
 1. a refrigerant supply transmission line to at least two evaporator units and
 2. a low pressure return-suction line from the evaporator units to appropriate refrigerant recirculation apparatus; G. means for receiving the recirculating the liquid refrigerant received from the evaporators; H. means for separating out the gaseous portion of the returning refrigerant and compressing it into a hot gas for hot gas defrosting of the several evaporator units; I. timer controlled means for selectively shutting off the refrigerant supply to that part of the evaporator units selected for defrosting; J. timer controlled means for closing off the usual evaporator return line from the evaporators being defrosted to the refrigerant recirculation apparatus; K. control means for routing compressed hot gas into the large diameter refrigerant transmission line to the evaporator units selected for defrosting during the defrost cycle; and L. control means for rerouting the used defrost gas back to the refrigerant recirculation apparatus.
 2. a suction-collection manifold,
 2. a low pressure return-suction line from the evaporator units to appropriate refrigerant recirculation apparatus; G. means for receiving the recirculating the liquid refrigerant received from the evaporators; H. means for separating out the gaseous portion of the returning refrigerant and compressing it into a hot gas for hot gas defrosting of the several evaporator units; I. timer controlled means for selectively shutting off the refrigerant supply to that part of the evaporator units selected for defrosting; J. timer controlled means for closing off the usual evaporator return line from the evaporators being defrosted to the refrigerant recirculation apparatus; K. control means for routing compressed hot gas into the large diameter refrigerant transmission line to the evaporator units selected for defrosting during the defrost cycle; and L. control means for rerouting the used defrost gas back to the refrigerant recirculation apparatus.
 2. The improved system of combination refrigeration and hot gas defrosting apparatus described in claim 1 in which the controlled and apportioning and division of hot gas between the evaporator and the drain pan heating coil during the defrost cycle is accomplished by meAns of sized control orifices in each of the parallel branch lines by which defrost gas is released into the several lines to be defrosted.
 2. an input into said surge drum from the refrigerant low pressure suction return lines from the evaporator units,
 2. a large diameter insulated low pressure refrigerant return-suction line from the evaporator units to appropriate refrigerant recirculation apparatus; H. refrigerant recirculation apparatus including
 2. a liquid refrigerant pump to supply liquid refrigerant to the several evaporator units with a. input connections from said surge drum and pump receiver and b. output leads to the refrigerant transmission supply lines to each of the several evaporator units to be supplied; I. a dry gas compressor
 2. with compressor discharge line connections to supply pressurized hot gas to a. a condenser system and b. to the hot gas defrost leads to the evaporator units; J. a high pressure condenser and receiver system with its input connected to the hot gas compressor discharge line and the output from said high pressure receiver reservoir connected back to the return liquid input into the surge drum and pump receiver; K. a defrost cycle control system for each system of evaporator units with said defrost cycle control system having
 2. a pressure operated relief valve in a defrost cross line between the closed off liquid refrigerant supply line and the low pressure suction return line by which the defrost gas is routed back to the surge drum and pump receiver for further recycling.
 2. a suction-collection manifold,
 3. a plurality of evaporation coils connected between the distribution manifold and
 3. a gas only output suction supply line from the upper portion of the surge drum with said gas output supply line leading to a hot gas compressor,
 3. The improved system of combination refrigeration and hot gas defrosting apparatus described in claim 1 in which the hot gas line and low pressure return-suction line from the evaporator unit is a large diameter pipe insulated through at least that part of its length that is inside of the refrigeration chamber to better protect said line from breaks precipitated by shock and extreme differences between internal and external temperature during the defrost process.
 3. a plurality of evaporation coils connected between the distribution manifold and the collection manifold and
 4. flow control orifices between each of the evaporation coils and one of the manifolds; B. a defrost drip-drain pan situated below the evaporator; C. a drain pan heating coil connected in parallel with the refrigerant leads to and from said evaporator unit; D. check valve means in the connecting lines to the drain pan heating coil for automatically preventing flow of refrigerant through the drain pan heating coil during refrigeration cycle while permitting the flow of hot gas in the reverse direction during defrost cycle; E. control means of apportioning the division of hot gas supply between the evaporator and the drain pan heating coil during the defrost cycle; F. a two pipe system of refrigerant supply lines into the refrigeration chamber comprising
 4. The improved system of combination refrigeration and hot gas defrosting apparatus described in claim 1 in which the refrigerant recirculation apparatus includes: A. a surge drum and pump receiver adapted to separate liquid refrigerant and gas having
 4. a metered liquid input into said surge drum from liquid return supply means from a condenser and high pressure receiver off of the hot gas compressor discharge line, and
 4. sized flow control orifices between each of the evaporation coils and one of the manifolds; C. a defrost drip-drain pan situated below the evaporator; D. a drain pan heating coil connected in parallel with the refrigerant leads to and from the associated evaporator unit; E. check valve means in the defrost gas line to the drain pan heating coil for automatically preventing flow of refrigerant through the drip pan heating coil during refrigeration cycle while permitting the flow of hot gas in the reverse direction during defrost cycle; F. sized orifice control means of apportioning the division of hot gas supply between the evaporator and the associated drain pan heating coil during the defrost cycle; G. a two pipe system of refrigerant supply lines intO the refrigeration chamber comprising
 5. a float actuated supply valve to meter and maintain a constant level of liquid refrigerant in said surge drum; and B. a liquid refrigerant pump to supply liquid refrigerant to the several evaporator units with a. input connections from said surge drum and pump receiver and b. output leads to the refrigerant transmission supply lines to each of the several evaporator units to be supplied.
 5. The improved system of combination refrigeration and hot gas defrosting apparatus described in claim 1 in which the plurality of evaporator units are divided into at least two systems of evaporators with the evaporator units within each system connected in parallel.
 6. The improved system of combination refrigeration and hot gas defrosting apparatus described in claim 5 with at least two sets of time clock control means and associated control valves actuating the controlling alternating cycles of refrigeration and defrosting in each system of evaporator units.
 7. The improved system of combination refrigeration and hot gas defrosting apparatus described in claim 6 in which the several time clock control means for the several evaporator systems are programmed in such manner that only one system of evaporators is defrosted at a time.
 8. An improved combination refrigeration and hot gas defrosting system comprising: A. an insulated refrigeration chamber; B. a plurality of refrigeration evaporator units situated in said refrigeration chamber with each of said evaporators being provided with
 9. The improved system of combination refrigeration and hot gas defrosting apparatus described in claim 8 in which the plurality of evaporator unit are divided into at least two systems of evaporators with the evaporator units within each system connected in parallel.
 10. The improved system of combination refrigeration and hot gas defrosting apparatus described in claim 9 with at least two sets of time clock control means and associated control valves separately actuating and controlling alternating cycles of refrigeration and defrosting in each system of evaporator units.
 11. The improved system of combination refrigeration and hot gas defrosting apparatus described in claim 10 in which the several time clock control means for the several evaporator systems are programed in such manner that only one system of evaporators is defrosted at a time. 